22 EXRAPHIDIAN CHARACTER OF WOLFFIA. 
Hab. Haud rara ad rupium fissuras, etiam in aridis maritimis in- 
sula Selvagem grande dicta?. Floret Februario, Martio. 
Obs. Pulcherrima species. Habitu externo a congeneribus valde 
distincta. 
In honorem clariss. Rev. R. T. Lowe, florae et faunae Oceani Atlan- 
tici insularum perscrutatoris insignis, necnon exactissimi descriptoris 
grato animo amice dedicavi. 
[I have not seen at present specimens of the above plant, but, relying impli- 
citly on the accuracy of the foregoing elegant and excellent description, I havo 
no doubt of its being perfectly distinct from every other Madeiran, Canarian, 
or Cape Verde species hitherto recorded. It seems to be allied to Sedum cceru- 
leum, Yahl (Sims in Bot. Mag. t. 2224), and may perhaps eventually prove to 
be better placed in Sedum than in Sempervivum. — R. T. L.] 
EXRAPHIDIAN CHARACTER OF WOLFFIA. 
By George Gulliver, F.R.S. 
In the last number of the ■ Journal of Botany I have indicated that 
a further examination of Wolffia would be interesting. 
Had Sir William Jackson Hooker, and other eminent botanists who 
regarded JFolffia arrhiza as nothing but the young state of Lemna 
minor, compared the cells of these two species, this error might have 
been avoided ; for, besides the difference between the cells of the epi- 
dermis, so well depicted by Hoffmann, I have shown, by an engraving, 
in the number of this Journal for last December, that while the raphides 
of Lemna minor are obvious and abundant, JFolffia arrhiza is destitute 
of them ; and since that sketch of these plants was printed, I have 
found that the raphidian character is easily seen, under an achromatic 
object-glass of half an inch focal length, even in the smallest voung 
fronds of Lemna minor, so that this diagnostic character is likely to 
prove always available and useful. 
Now JFolffia Brasiliensis, like JF. arrhiza, proves also to be an ex- 
raphidian plant ; and thus these two species agree well with each other, 
and both alike differ as remarkably from Lemna minor. 
In this single point of view, JFolffia approaches more nearly than 
Lemna to Acotyledons. I have in vain searched many of our Ferns, 
Mosses, and their allies, for the raphides which I have found in all the 
British species of Lemna and in the exotic PiaLia. But our knowledge of 
s* 
